1. Field of the Invention
The present invention relates to an automobile air conditioner having a motor-driven compressor driven by an electric power from a direct-current power source.
2. Description of the Related Art
FIG. 9 is a block diagram of a conventional automobile air conditioner having a motor-driven compressor driven by an electric power from a direct-current power source. To drive a motor-driven compressor 14, an output unit 11 (generally known as inverter circuit) converts a direct-current supply voltage into an alternating-current driving voltage. A capacitor 7 is provided to suppress the ripple voltage of the direct-current power source. When a circuit breaker 3 is closed, this capacitor 7 of a large capacity is charged from a battery 1 by way of fuse 2, circuit breaker 3, diode 4 and resistor 5. The diode 4 is intended to protect the circuit so that the current may not flow in case the battery 1 is connected in wrong polarity.
A controller 10 receives a command for operating the motor-driven compressor 14 from an air conditioner controller 12, and confirms the charge voltage of the capacitor 7 detected by a voltage detector 8. When the voltage of the capacitor 7 has reached a specified value, the controller 10 closes a relay 6. Consequently, the output unit 11 provides with a driving voltage, and drives the motor-driven compressor 14. A 12-volt power source of the controller 10 is supplied from the power source 13. Although not shown, a switching power supply unit 9 converts the voltage of the battery 1, and supplies the converted voltage to the output unit 11 and voltage detector 8.
On the other hand, when receiving a stop command of the motor-driven compressor 14 from the air conditioner controller 12, the controller 10 stops the output from the output unit 11, and opens the relay 6.
In the conventional configuration, when checking or repairing the air conditioner, first, the circuit breaker 3 is opened, and the capacitor 7 is allowed to discharge. After the electric charge is discharged sufficiently, checking or repairing can be started. In this case, the electric charge accumulated in the capacitor 7 is discharged as it is consumed by the switching power supply unit 9. This discharging, however, takes a long time because the load is light.
To shorten the discharge time, with the circuit breaker 3 being opened, the controller 10 can discharge the capacitor 7 by driving the motor-driven compressor 14 by means of the output unit 11. In this case, the discharge speed is faster, but the following problems are involved.
1. The motor-driven compressor 14 must be connected.
2. Complicated software for driving the motor-driven compressor 14 is needed. It is difficult to realize this method by a hardware circuit instead of using this software.
3. The power source 13 must be connected to the controller 10.
Moreover, a method of using other discharge resistance is known, but this method requires a discharge resistor of a large current rating, and hence the equipment size is increased.
The present invention is devised in the light of such conventional problems. The automobile air conditioner of the invention comprises a direct-current power source, a power feeding device connected in series to the direct-current power source, a switching device connected in parallel to the power feeding device, a first capacitor charged through the power feeding device from the direct-current power source, an output unit for driving a motor-driven compressor for air conditioning by receiving electric power from the switching device, a discharge circuit for discharging the electric charge in the first capacitor through the power feeding device, and a controller for controlling the discharge circuit.